tests: add test-fdmon-epoll

Test aio_disable_external(), which switches from fdmon-epoll back to
fdmon-poll. This resulted in an assertion failure that was fixed in the
previous patch.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20200915120339.702938-3-stefanha@redhat.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index 534fb4c..5eed1e6 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2132,6 +2132,7 @@
 F: include/block/aio.h
 F: include/block/aio-wait.h
 F: scripts/qemugdb/aio.py
+F: tests/test-fdmon-epoll.c
 T: git https://github.com/stefanha/qemu.git block
 
 Block SCSI subsystem